Chemical gas-releasing (blowing) agents, such as azodicarbonamide, p-toluenesulfonylhydrazide, p,p'-oxybis(benzenesulfonylhydrazide), and dinitrosopentamethylenetetramine, are well known in the art. These chemical blowing agents are generally solid compounds, which must be thermally decomposed in order to generate gaseous products and to facilitate, in a foaming process, the expansion needed for producing a cellular body. These blowing agents generally are useful over a limited temperature range.
Disadvantages of these commercial chemical blowing agents are that they generally must be thermally decomposed by heating to their specific decomposition temperature, and, subsequently, held for a specific length of time in order for gas-generation to occur. This gas-generation can provide the necessary expansion of a polymer medium which can result in the formation of a cellular body by one of the known processes, such as low pressure molding, high pressure molding, and continuous extrusion.
A disadvantage of thermally activated blowing agents is their limited useful temperature range and the difficulty in balancing the gas-generation or expansion with the correct fluidity-temperature relationship of the polymer matrix. The use of a specific chemical blowing agent outside of its decomposition range (for example, too high a temperature) will result in a poorly structured cellular body. Too low a temperature will yeild no gas-generation or expansion.
Tertiary-alkylhydrazinium salts and/or carbonylhydrazines have been used as blowing agents in foaming and crosslinking systems. U.S. Pat. No. 4,393,148 discloses the foaming and curing (crosslinking) of an unsaturated polyester resin at ambient temperatures using a peroxide curing agent, an iron or copper metal salt promoter, and a t-alkylhydrazinium salt blowing agent. U.S. Pat. No. 4,435,525 also discloses the foaming and curing of an unsaturated polyester resin at ambient temperatures using a carbonylhydrazine blowing agent. Published European patent application No. 0048050 discloses the foaming and curing of an unsaturated polyester resin using a t-alkyl hydrazine blowing agent.